The present invention relates generally to navigation systems and more specifically to an improved navigation system for calculating an alternate route.
Navigation systems generally provide a recommended route from an origin to a desired destination. Generally, the origin and desired destination are selected from a large database of roads stored in a mass media storage device, such as a CD ROM, which includes the roads in the area to be traveled by the user. The navigation system typically includes one or more position determining devices, such as a GPS (Global Positioning System) receiver, which indicates the current position of the vehicle relative to the database. The navigation system typically defines the current vehicle location as the origin for calculating a route. The navigation system then determines a route from the origin to the desired destination utilizing algorithms well-known to those in the art and currently in use in many navigation systems. The navigation system selects a recommended route from the origin to the desired destination based upon xe2x80x9ccostxe2x80x9d values associated with each segment of road in the road database, such as the estimated time of travel through the road segment. The navigation system determines the route with the lowest total estimated time of travel to the desired destination. The recommended route is then displayed to the user as a map showing the origin and desired destination and highlighting the recommended route. The navigation system then displays the current position of the vehicle and turn-by-turn instructions to the driver, guiding the driver to the desired destination.
If the navigation system also includes a receiver for receiving information relating to traffic congestion of certain road segments, the navigation system recalculates the estimated times of travel for the road segments and may determine that an alternate route would be preferable. Similarly, while en route to a first desired destination, a driver may decide instead to travel to a second destination. In either situation, because the known navigation systems utilize the current vehicle location as the origin, the vehicle is no longer at the origin by the time the route is calculated and then displayed to the driver . As a result, the driver may have already missed an initial maneuver or may be tempted to attempt a rushed maneuver. This causes not only obvious safety concerns but also causes anxiety and discomfort to the driver utilizing the navigation system.
The present invention provides a navigation system which selects a point on the first recommended route as an xe2x80x9coriginxe2x80x9d for the second recommended route. The navigation system includes a CPU, a database of roads to be travelled by the user, position-determining devices, and a user input device.
The navigation system calculates a first route according to known algorithms to a first selected destination. As the navigation system guides the driver turn-by-turn toward the first destination along the first recommended route, there are situations where the navigation system of the present invention calculates a second recommended route. In such situations, the point selected as the xe2x80x9coriginxe2x80x9d for the second recommended route is an intermediate point lying on the first route between the current vehicle location and the first destination. Depending upon whether the vehicle is travelling a highway or sidestreet, the actual or expected speed of the vehicle, and what type of initial maneuver is required, the intermediate point is selected to give the driver the necessary lead time to make the initial maneuver onto the second recommended route.
One situation where a second recommended route is calculated by the navigation system is where the second recommended route is an alternate route to the first destination which avoids a congested road segment. Another situation is where the second route also leads to a second destination rather than the first destination, such as when the driver decides to travel to the second destination while en route to the first destination.